Viscose process



United States Patent du Pont de Nemours and Company, Wilmington, Del.,

a corporation of Delaware No Drawing. Application April 26, 1955 Serial No. 504,120

8 Claims. (CI. 18-54) This invention relates to the manufacture of regenerated cellulose structures by the viscose process. More particularly, it relates to improvements in the process of spinning modified viscose solutions for the production of regenerated cellulose articles.

7 It is known that when viscose is extruded into acid coagulating baths containing zinc salts in the presence of certain nitrogen-containing organic compounds, regenerated cellulose yarns of vastly improved physical properties are produced. The filaments which make up the yarn are characterized by unusual cross section and surface features. The filaments display no appreciable crenulations so that the surface is relatively smooth. The ratio of skin to core measured radially in a typical cross section is greater than one and in many cases the filament cross-section may display only skin. (The greater the amountof skin, the greater is the improvement in properties.) Furthermore, the swelling of both the freshly spun gel yarn and the yarn after drying (the secondary swelling) is reduced. These characteristics, it has been found, correlate with the high tenacity and:high fatigue resistance in yarns and cords produced from the filaments. The nitrogen-containing organic compounds sug gested as modifiers for producing these exceptional yarns include certain classes of amines, quaternary ammonium compounds and dithiocarbamates. These compounds are described in U.S. Patents 2,535,044, 2,535,045 and 2,536,014, all issued to N. L. Cox on December 26, 1950, and 2,696,423, issued December 7, 1954, to M. A. Dietrich.

While producing outstanding regenerated cellulose yarns and cords, coagulation modifiers seem to provide spinning difiiculties, particularly bothersome at spinning speeds of 60 yards per minute and higher. Thus, an amount of modifier that is sufiicient to produce a substantially all-skin filament tends to cause yarn breaks with accompanying machine breakdowns after relatively short spinning periods. Decreasing the amount of modifier tends to prolong spinningtime, but yields a correspondingly inferior product and, more important, yields a nonuniform product.

It is accordingly an object of this invention to provide a viscose process employing a coagulation modifier that avoids spinning difiiculties without sacrificing yarn and cord properties. A further object is to provide a process wherein filaments, fibers, yarns and cords of uniformly high quality are produced at high spinning speeds. Other objects will appear hereinafter. I

The objects of this invention are accomplished by preparing a viscose spinning solution containing a soluble salt of a N-methylcyclohexyldithiocarbamic acid, preferably sodium N-methylcyclohexyldithiocarbamate, and extruding the viscose at a temperature of 15 C. to 60 C. into a spinning bath containing 4% to 12% sulfuric acid,

% to 25% sodium sulfate, 2% to 15% zinc sulfate and; nitrogen; the amount of dithiocarbamate in theviscose;

'ice

and the amount of the nitrogen in the bath being critically related according to the following formula:

X=(.084i.012) (4.8 X 10- Y where X represents the percentage of the N-methylcyclohexyldithiocarbamate in the viscose; and Y represents the nitrogen content of the spinning bath expressed as parts per million.

All percentages are by weight.

Preferably, the amount of the salt of N-methylcyclohexyldithiocarbamic acid in the viscose, the nitrogen content of the bath, the extrusion temperature of the viscose and the amount of zinc sulfate in the bath are related according to the following formula:

X: (0841.012) (4.8 X 10 Y where X represents the concentration of dithiocarbamate salt in the viscose in weight percent; Y represents the nitrogen content of the spinning bath in parts per million; Z represents the concentration of zinc sulfate in the spinning bath in weight percent; S represents the con-, centration of sulfuric acid in the spinning bath inweight percent; and T represents the viscose grees centigrade.

The use of a salt of N-methylcyclohexyldithiooarbaudio acid as a coagulation modifier, although not specifically disclosed or claimed, is within the scope of U.S. Patent 2,696,423.

2,535,044. In this latter patent, a monoamine is added to the viscose solution prior to spinning. Some of the monoamines encompassed by the patent, by reaction with the ingredients of the xanthating mixture, namely alkali cellulose and carbon disulfide, will form the salt of the; However, it was found' Unless otherwise stated, all percentages in the examples,-

the discussion and the claims are by weight. Example I sets forth the best mode contemplated for carrying out the invention. The other examples set forth specific embodiments of the process invented. The examples are not to be construed in any sense as limitative of the invention.

The properties of the yarns and cords produced by the process of the invention are presented. In this presentation, the following symbols are used:

T is dry tenacity in grams/denier T is wet tenacity in grams/denier T is loop tenacity in grams/denier EdwJ are percent elongations, dry, wet and loop T is conditioned tenacity in grams/denier T,, is oven-dry tenacity in grams/denier E lbs. is percent elongation when applied D.B. fatigue is the number of minutes required to breakthe cord with the dynamically balanced fatigue tester The measurements are conventional with the possible: exception of the DB. fatigue test. Inthis test, acorcl."

Patented June 23, 1959' temperature in, de-

Spinning in the presence of the salt is also encompassed, although not specifically, by U.S. Patent is conditioned for 48 hours at 24 C. and 54% relative humidity and clamped in jaws set 16.75 inches apart. A load of 1 gram/denier is applied and the cord is brought to 100 C. while in place in the machine for about one-half hour. The yarns are then oscillated to stretch the cord 3000 times per minute using a stroke of 0.24 inches. The number of minutes survived before breaking is recorded as the DB. fatigue.

EXAMPLE I A viscose spinning solution containing 6.25% cellulose, 5.75% alkali calculated as sodium hydroxide and 06% sodium N-rnethylcyclohexyldithiocarbamate was prepared from wood pulp sheets using a total of about 3.8% carbon disulfide based on the weight of the airdried pulp.

The addition of carbon disulfide was split between the baratte and the mixer. 26.6% based on the air-dried pulp weight was added in the baratte and ll.4% in the mixer. Thus, 70% of the xanthation occurred in the baratte and 30% in the mixer.

Specifically the wood pulp sheets were soaked in caustic alkali to form alkali cellulose. Excess caustic was drained and pressed from the sheets. The sheets were shredded and aged to provide the desired viscosity in the ultimately prepared viscose solution. The shredded alkali cellulose was dropped into a baratte where the first xanthation step occurred. The partially xanthated alkali cellulose was added to the mixer, which mixer contained dilute aqueous caustic and the sodium dithiocarbamate. After mixing for about 20 minutes the remaining quantity of carbon disulfide was added to complete xanthation.

The solution was filtered, deaerated and permitted to ripen to a salt index of about 17 and to attain a viscosity of 32.1 stokes. Prior to spinning, the solution was passed through a coil-type heater immersed in a tank of hot water. The solution was thus heated to a temperature of about 44 C. and extruded into a bath maintained at a temperature of about 60 C. containing 9.5% sulfuric acid, 17.3% sodium sulfate and 9.5% zinc sulfate.

Upon extrusion, the filaments were led through a trumpet-like tube located in the bath and then by means of tension rollers in the bath the filaments were stretched in gradual increments about 70% to 80%. After leaving the bath the filaments passed over two feed wheels in succession to impose an additional 20% stretch on the filaments. During this latter stretching, the filaments were treated with a 2% sulfuric acid solution at a temperature of about 90 C. The filaments were then led into a rotating bucket at a speed of 100 yards per minute to form cakes. The cakes were purified, slashed and processed into cords in the conventional manner.

Spinning at 100 yards per minute while the bath content measured 200 parts per million of nitrogen was extremely difficult. The breaks in the yarn averaged about 600 per 100 spinning positions during a 24-hour period. However, when the formula of the present invention was applied, the results were quite different. Substituting the sodium dithiocarbamate concentration of the viscose, the zinc sulfate concentration of the bath and the temperature of the viscose solution in the formula:

X:(.084i.012)(4.8 l )Y (.025i.003) (9.5S)+(.0006i.00007) (44-T) indicated that the bath should contain about 42 parts per million of nitrogen.

With 42 parts per million of nitrogen in the bath, spinning at 100 yards per minute provided no appreciable difficulty. The number of yarn breaks was reduced to less than 50 compared to the previous 600. This nitrogen content was maintained at 42 parts per million .4 by circulating the bath through a bed of activated carbon to remove any excess.

The filament cross sections were examined under a microscope. The filaments displayed to 100% skin. This high skin thickness prevailed uniformly throughout the length of the yarn. The yarn and cord properties are presented below:

Yarn properties was added in the baratte and only 022% sodium N- methylcyclohexyldithiocarbamate was added to the viscose solution. In conformance with the formula, the nitrogen content of the bath was adjusted to 136 parts per million. Spinning difficulties were substantially absent and results were essentially those given in Example l.

EXAMPLE III Example I was re-run except that 40% carbon disulfide (based on the air-dried pulp) was used, 70% in the baratte and 30% in the mixer, and .079% sodium N-methylcyclohexyldithiocarbamate was added to the viscose solution. In conformance with the formula, the nitrogen content of the bath was adjusted to 10 parts per million. Spinning difficulties were substantially absent and results were assentially those given in Example 1.

EXAMPLE IV Example II was repeated except that .035%, based on the weight of the viscose, of N-methylcyclohexylamine, having a purity of was added at the beginning of the mixing cycle. Analysis of the viscose at spinning showed the presence of 0.061% sodium N-methylcyclohexyldithiocarbamate, indicating that over 98% of the N-methylcyclohexylamine had been converted to the dithiocarbamate. Spinning was carried out with 42 parts per million of nitrogen in the bath, as required by the formula. Spinning difficulties were substantially absent, and the yarn and cord properties Were equivalent to those shown in. Example I.

EXAMPLE V Example 11 was repeated except that 36% carbon disulfide (based on the air-dried pulp) was added to the baratte and 0.08% of sodium N-methylcyclohexyldithiocarbamate was added to the viscose. The viscose was extruded at a temperature of 22 C. In conformance with the formula the concentration of nitrogen in the bath was adjusted to 35 parts per million. No spinning difficulty was encountered. Yarn and cord properties are shown below:

Yarn properties Denier Ta Tw T1 Ea Ew E1 Cord properties Denier To Eu nu. ad. lg g EXAMPLE VI EXAMPLE VII A viscose spinning solution containing 5.0% combined cellulose, 5.5% total alkali, calculated as sodium hydioxide and sodium N-methylcyclohexyldithiocarbamate was prepared from sheets of cotton linters pulp in the conventional manner using about 35% carbon disulfide based on the weight of the air-dried pulp.

The solution was filtered, deaerated and permitted to ripen to a salt index of about 1 1 and to attain a viscosity of about 21 stokes. The solution, at a temperature of about 20 C. was extruded into a bath maintained at a temperature of 63 C. containing 8.9% sulfuric acid, 8.0% zinc sulfate and 17.5% sodium sulfate.

' Upon extrusion, the filaments were led through a trumpet-like tube located in the bath and then by means of tension rollers in the bath the filaments were stretched a total of about 75%. After passing through the bath, the total bath travel being about 100 inches, the yarn was led to a rotating bobbin and Wound up in the conventional manner at an average speed of 62 yards per minute. 'Ihe yarn'was th'en purified, slashed and processed into cords in the conventional manner.

Spinning at 62 yards per minute when the viscose contained 0.072% of sodium N-methylcyclohexyldithiocarbamate was very difficult. The breaks in the yarn averaged about'600 per hundred spinningpositions during a 24'hour period. During this period the mechanical quality of the yarn was very poor. Examination of the yarn revealed about 200 defects (broken filaments) per pound of yarn. In short, the level of spinability and quality was not commercially acceptable. However, when the sodium-N-methylcyclohexyldithiocarbamate in the viscose was adjusted to a level of 0.036% in accordance with the formula:

X=(0.084i0.012) 4.s Y-

(0025:0003)(9.5S)+(0.0006i0.00007)(44-1 Y 0.007:0.000s) 9.s-z

the results were much improved. Yarn breaks were reduced to about 40 per 100 spinning position during a 24 hour period and the mechanical quality was improved to a level of 4 defects per pound of yarn.

When the concentration of sodium N-methylcyclohexyldithiocarbamate in the viscose was maintained at 0.036% it was found that the nitrogen content of the bath remained constant at about 120 parts per million without any addition of, nitrogen. Thus, it was found un necessary to remove any nitrogen from the bath and the need for a recovery'system was eliminated.

The filament cross-sections were examined under a microscope. The filaments displayed 85% or more skin. This 'high skin thickness prevailed uniformly throughout the length of the yarn. The yarn and cord properties are given below:

tion yields improvements with ripe viscoses, it is prefer- Yarn properties Denier Ts ,T- T1 Ed E. El

Cord properties Denier' Tls E15 u. Ton. aig

In the process of this invention the alkali cellulose is prepared in the conventional manner. Sheets of wood pulp or cotton linters pulp may be used. They are first soaked in sodium hydroxide solution; excess alkali is drained and pressed from the sheets; and the resulting alkalicellulose is shredded and aged. The shredded,

alkali cellulose is then dropped into a rotatable drum called a baratte where xanthation occurs.

The alkali cellulose may be completely xanthated in the baratte or partially xanthated in the baratte and Splitting xanthation so that not copending US. application, Serial No. 351,592 filed April 28, 1953, to A. Robertson, now United States Patent 2,801,998. the amount of carbon disulfide'used is at least 28% based on the air-dried pulp. The preferable amount of carbon disulfide is 35% to 45%.

The xanthated or partially xanthated alkali cellulose is then added to a tank where it is mixed with a measured quantity of dilute aqueous sodium hydroxide solution. The amount of sodium hydroxide solution is sufi'icient to provide a final viscose solution containing 4% to 15% celluloseiand 4% to 8% total alkali calculated as sodium hydroxide. An amount of the salt of the N-methylcyclo hexyldithiocarbamic acid up to about 0.11% of theweight of the final viscose solution is preferably added to .the viscose during the mixing cycle. It may also be introduced into the viscose by adding it to any of the materials used in preparing the viscose.

situ may be added. If desired, the, salt may be mixed into the viscose at some time after the normal mixingperiod but prior to spinning.

In the examples, sodium N-methylcyclohexyldithiocarbamate has been used. However, any salt of N-methylcyclohexyldithiocarbamic acid may be used. The proeise amount used in the viscose solution depends very critically on the nitrogen content of the spinning bath.

The importance of adjusting the concentrations of the' salt in the viscose and nitrogen in the bath according to a critical formula is illustrated by the foregoing examples.

The viscose solution is filtered, deaerated and permitted to ripen at a temperature of about 18 C. to a salt index of at least 5. While the process of this invenable to restrict ripening and spin the viscose in an unripened or a partially ripened state (at a salt index of 14 to 18).

Prior to spinning, the viscose may be heated by means a of a small oil-bath heat exchanger placed between the spinning pump and the spinneret. Heating may also be accomplished by other suitable heating medium such as steam, hot water, or coagulating bath; or an electric I heating unit may be inserted in the pipe. 7 p

.The viscose spinning solution at a temperature above sulfuric acid; 5% to 25 preferably 13% to 20%, so-

dium sulfate; 2% to 15%, preferably 5% to 15%, zine In either conventional or split xanthation,

The dithiocarbamate salt itself or the monoamine to form the salt in sulfate and a small amount of an effective anticratering agent. In addition, the bath contains nitrogen, some of which may arise from the decomposition of the N-methylcyclohexyldithiocarbamate salt and some of which may be added, in an amount which is related to the amount of- N-rnethylcyclohexyldithiocarbamate in the viscose according to he critical formula given previously.

The adjustment of the nitrogen content of the bath may be accomplished in several ways. When equilibrium conditions have been established, any excess of nitrogen may be removed by adsorption on carbon or the like. The bath, which is usually recycled and bolstered with additions of sulfuric acid, sodium sulfate and zinc sulfate, may be led through a bed of activated carbon where the excess nitrogen is removed. If insufiicient nitrogen is present, nitrogen may be added as the dithiocarbamate or in other forms to the bath during recycling or directly to the bath tank. A preferred mode of operation consists of adjusting the addition of dithiocarbamate to the viscose, the rate of extrusion and the rate of recycling and replenishing bath so that when equilibrium is established, the concentration of nitrogen in the bath corresponds to that dictated by the formula. This latter system has the advantage of not requiring extra equipment and not requiring substantial maintenance once equilibrium is established.

The filaments may be extruded through a spinning tube to confine the filaments in the critical stage of formation as described in US. Patent 2,440,057 to F. R. Millhiser. After extrusion, the filaments travel through about 25 to 150 inches in the primary bath where they may be confined to a small area by means of a multiple roller set-up. The rollers are designed to apply tension to the traveling filaments in gradual increments and thereby orient them while they are still plastic. A preferred method is to apply part of the stretch beyond the primary bath by passing the filaments through a secondary bath or shower located between two feed wheels. The secondary bath may consist simply of water or of dilute (1% to 4%) acid or diluted coagulating bath at a temperature between 50 C. and 100 C. Total stretches of over 70% are used for producing high tenacity yarns and as low as 30% may be used for textile yarns. From the last feed wheel, the yarn is fed at a speed of 50 to 200 yards per minute, preferably at or above 90 yards per minute into a rotating bucket to form a cake. As a cake, the yarn is washed, dried, unwound and slashed. The slashing operation is well known and consists of stretching the yarn and applying a lubricating solution. The process of collecting the yarn in a bucket is called the bucket process. However, the yarn may be collected on a bobbin as shown in Example Vli or it may be led directly through the aftertreatments as in the so-called continuous processes.

The main advantage of the process is that it provides a way of achieving high speed when spinning so-called modified yarns. By distributing the modifier between the viscose solution and the spinning bath in accordance with a critical formula, vastly improved yarns can be prepared at spinning speeds of 60 yards per minute and higher, preferably above 90 yards per minute. Heretofore, the speed of spinning these yarns had been limited by the difficulties encountered during spinning. Thus, the process, by permitting spinning at substantially high speeds, reduces the cost of producing the improved yarns.

Further economies are achieved by the preferred use of relatively unripe viscose solutions and the use of the preferred split xanthation process. The unripe viscose requires less equipment and less time for ripening. The split xanthation process shortens the xanthation cycle and provides barattes that are easier to clean and to ventilate.

The improved yarns obtainable through the process of this invention can be used instead of regular regenerated cellulose yarns for any purpose Where the latter find ap plication, more particularly in the textile and tire cord industries. Textile fabrics made from these yarns, either continuous filament or staple, have high strength; resist soiling and abrasion; and are easily laundered. Fabrics for automobile and truck tires utilize the high tenacity and the high fatigue resistance of the yarns and cords to prolong the lives of the tires. These fabrics are also use ful in reinforcing other rubber goods such as commercial V-belts and the like.

As many widely. different embodiments may be made without departing from the spirit and scope of the invention, it is understood that the invention is not limited except as defined in the appended claims.

Having fully disclosed the invention, I claim:

1. In a process of spinning a viscose filament-forming solution to form regenerated cellulose filaments, the improvement which comprises extruding a viscose solution containing a soluble salt of N-methylcyclohexyldithiocarbamic acid through the orifices of a spinneret into a spinning bath containing 4% to 12% by weight sulfuric acid, 5% to 25 by weight sodium sulfate, 2% to 15% by weight zinc sulfate and nitrogen, in the form of a nitrogen-containing organic compound, to form filaments and thereafter collecting the filaments at a speed of at least about 60 yards per minute; the amount of the salt of N-methylcyclohexyldithiocarbarnic acid in the viscose solution and the amount of nitrogen in the bath being related according to the following formula:

where X represents the concentration of the soluble salt of N-methylcyclohexyldithiocarbamic acid in the viscose solution in Weight percent, and Y represents the nitrogen content of the spinning bath in parts per million.

2. A process as in claim 1 wherein the soluble salt of N-methylcyclohexyldithiocarbamic acid is sodium N- methylcyclohexyldithiocarbamate.

3. A process as in claim 1 wherein the filaments are spun at a speed of at least yards per minute.

4. In a process of spinning a viscose filament-forming solution to form regenerated cellulose filaments, the improvement which comprises extruding a viscose solution containing a soluble salt of N-methylcyclohexyldithiocarbamic acid through the orifices of a spinneret at a temperature of 15 C. to 60 C. into a spinning bath containing 4% to 12% by weight sulfuric acid, 13% to 25% by weight sodium sulfate, 2% to 15% by weight zinc sulfate and nitrogen, in the form of a nitrogen-containing organic compound, to form filaments and thereafter collecting the resulting filaments at a speed of at least about 60 yards per minute; the amount of the salt of N-rnethylcyclohexyldithiocarbamic acid in the viscose solution, the amount of nitrogen in the spinning bath, the amount of zinc sulfate in the spinning bath and the extrusion temperature of the viscose solution being related according to the formula:

X: (.084i.0l2) (4.8 10" )Y where X represents the concentration of the soluble salt of N-methylcyclohexyldithiocarbamic acid in the viscose solution in weight percent; Y represents the nitrogen content of the spinning bath in parts per million; Z represents the concentration of zinc sulfate in the spinning bath in weight percent; S represents the concentration of sulfuric acid in the spinning bath in Weight percent; and T represents the viscose temperature in degrees Centigrade.

5. A process as in claim 4 wherein the soluble salt of N-methylcyclohexylditbiocarbamic acid is sodium N-= methylcyclohexyldithiocarbamate.

6. A process as in claim 4 wherein the filaments are spun at a speed of at least 90 yards per minute.

7. A process of spinning regenerated cellulose filaments which comprises extruding a viscose filament-forming solution at a salt index of 14 to 18 and at a temperature of 40 C. to 80 C. through the orifices of a spinneret, said viscose solution containing 4% to 15% cellulose, 4% to 8% caustic and sodium N-methylcyclohexyldithiocarbamate, into a spinning bath containing 6% to 10% sulfuric acid, 13% to 20% sodium sulfate, to 15% zinc sulfate and nitrogen, in the form of a nitrogen-containing organic compound; the amount of sodium N- methylcyclohexyldithiocarbamate in the viscose solution, the amount of nitrogen in the spinning bath, the amount of zinc sulfate in the spinning bath and the extrusion temperature of the viscose solution being related according to the formula:

X= (.084: :.0l2) (4.8 X Y (.025i.003) (9.5-S) (0006:.00007) (44-T) where X represents the concentration of the soluble salt of N-methylcyclohexyldithiocarbamic acid in the viscose solution in weight percent; Y represents the nitrogen content of the spinning bath in parts per million; Z represents the concentration of zinc sulfate in the spinning bath in weight percent; S represents the concentration of sulfuric acid in the spinning bath in weight percent; and T represents the viscose temperature in degrees centigrade; stretching the filaments over 70% and collecting the filaments at a rate of at least 90 yards per minute.

8. In a process of extruding a viscose solution containing a soluble salt of N-methylcyclohexyldithiocarbamic acid through the on'fice of a spinneret into a spinning bath containing 4% to 12% by weight sulfuric acid, 5% to 25% by weight sodium sulfate, 2% to 15% by weight Zinc sulfate and nitrogen in the form of N-methylcyclohexylamine, to form filaments and thereafter collecting the filaments at a speed above about yards per minute, the improvement which comprises removing nitrogen, in the form of a nitrogen-containing organic compound, from the bath as its value exceeds that given in the equation and adding nitrogen, in the form of a nitrogen-containing organic compound, to the bath as its value decreases below that given in the equation wherein each equation X represents the percentage of the N-methylcyclohexyldithiocarbamate in the viscose and Y represents the nitrogen content of the spinning bath expressed in parts per million.

References Cited in the file of this patent UNITED STATES PATENTS 2,364,407 Walker Dec. 5, 1944 2,536,014 Cox Dec. 26, 1950 2,535,044 Cox Dec. 26, 1950 2 D t i D 1 54 

1. IN A PROCESS OF SPINNING A VISCOSE FILAMENT-FORMING SOLUTION TO FORM REGENERATED CELLULOSE FILAMENTS, THE IMPROVEMENT WHICH COMPRISES EXTRUDING A VISCOSE SOLUTION CONTAINING A SOLUBLE SALT OF N-METHYLCYCLOHEXYLDITHIOCARBAMIC ACID THROUGH THE ORIFICES OF A SPINNERET INTO A SPINNING BATH CONTAINING 4% TO 12% BY WEIGHT SULFURIC ACID. 5% TO 25% BY WEIGHT SODIUM SULFATE, 2% TO 15% BY WEIGHT ZINC SULFATE AND NITROGEN, IN THE FORM OF A NITROGEEN-CONTAINING ORGANIC COMPOUND, TO FORM FILAMENTS AND THEREAFTTER COLLECTING THE FILAMENTS AT A SPEED OF AT LEAST ABOUT 60 YARDS PER MINUTE; THE AMOUNT OF THE SALT OF N-METHYLCYCLOHEXYLDITHIOCARBAMIC ACID IN THE VISCOSE SOLUTION AND THE AMOUNT OF NITROGEN IN THE BATH BEING RELATED ACCORDING TO THE FOLLOWING FORMULA: 